The long term goal of this research is to create a miniature bandage-size non-invasive deep tissue thermal sensor that is sensitive to changes in tissue temperature at depth in the body. The objective of this project is to develop a low cost and harmless new tool for long term monitoring of metabolic activity of human brown adipose tissue (BAT). The rationale for undertaking this development is that there is currently no effective and reliable method for continuous monitoring of energy expenditure of a distributed organ like Brown Adipose Tissue (BAT) which is present in small multifocal depots. We intend to accomplish our objective by pursuing the following three specific aims: Aim 1: Design and fabricate a miniature radiometric sensor suitable for non-invasive measurement of thermal irregularities within 4 cm of the tissue surface. This sensor will require development of: 1.1) appropriate anatomical, thermal and electromagnetic models of BAT, 1.2) low profile microwave antenna with effective coupling to typical BAT regions, and 1.3) low power consumption integrated chip electronics (e.g. HEMT preamplifier, power detector, ultralow loss MEM switch, precision A/D converter). Aim 2: Integrate all components optimized in Aim 1 into an adhesive bandage-size patch sensor including radiometer circuitry, EMI shielding, battery power source, and wireless telemetry link. This miniaturized multichip circuit mounted on the back side ground plane of the receive antenna will require optimization of power consumption, thermal stability, and wireless communication for remote recording of temperature change over long time periods (hours to days) Aim 3: Characterize performance of microwave radiometric sensor in terms of sensing volume, accuracy and stability of temperature measurements, EMI rejection, and error free telemetry. Quantify antenna radiation patterns of the monitoring and telemetry antennas, and quantify temperature sensitivity of the multiband radiometer as functions of target size and depth in tissue and difference above core temperature in multilayer BAT phantoms - in preparation for subsequent use in humans. The expected outcome is a lightweight, adhesive bandage encased, safe and painless thermal monitoring sensor useful for clinical studies requiring long term characterization of energy production or utilization in tissue. The resulting technology should translate readily to thermal monitoring applications beyond this grant.